math_fact: 8439 is a value of n for which n and 8n together use each digit 1-9 exactly once.
trivia: 8439 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
historical_date: February 7th is the day in 1894 that the Cripple Creek miner's strike, led by the Western Federation of Miners, begins in Cripple Creek, Colorado.